#include<iostream>
#include<map>
#include<vector>
#include<set>
#include<string>
using std::endl;
using std::cout;
using std::map;
using std::set;
using std::vector;
using std::string;
class FOO{
public:
    FOO(const int &a)
    :_a(a)
    {}
private:
    FOO(const FOO&rhs) = delete;
private:
    int _a;
};

void test01(){
    //FOO fo = 2;//避免了隐式转换
    FOO fo(2);
    //FOO fo3  = fo;
}

int main(void){

}